1. Field of the Invention
The present invention relates to a recording apparatus and a recording method for performing light modulation recording, that is, data recording on a recording medium by a laser beam modulated by recording data.
2. Description of the Related Art
When performing light modulation recording on a recording medium such as an optical disk or the like, a laser emits light in pulses in order to perform thermal control for shaping a pit (mark) to be formed on the disk.
Specifically, a pulse waveform as a driving pulse for driving the laser is arranged, and the level (peak value) during each pulse period is controlled, thereby controlling the laser power and the laser irradiation time.
For example, data is written on disk media in which data can be written, namely, CD-recordable (CD-R) which is CD-write once (CD-WO) and CD-rewritable (CD-RW), at data writing speeds of xc3x971, xc3x972, and xc3x974 speeds. Laser emission control in accordance with the writing speed is performed as shown in FIGS. 14 and 15. The xc3x971 speed corresponds to 1.2 to 1.4 m/s, which is achieved by rotating a disk in a constant linear velocity (CLV) mode.
FIG. 14 shows a driving pulse generated when writing at a xc3x971 writing speed or a xc3x972 writing speed.
It is known that a CD system generates an EFM signal as recording data. The pulse duration of the EFM signal is specified within a range of 3T to 11T, as shown in FIG. 14. The letter xe2x80x9cTxe2x80x9d corresponds to one channel clock period.
Based on the EFM signal, an equalized EFM signal (hereinafter referred to as an xe2x80x9cEQEFM signalxe2x80x9d) is generated, as shown in FIG. 14. The EQEFM signal is used as a laser driving pulse.
In the example shown in FIG. 14, the EQEFM signal has a pulse which basically has a duration of (Nxe2x88x921)T compared with (N)T of the EFM pulse (in the drawing, xcex8=1T).
For example, concerning the EFM signal having a pulse duration of 4T, the EQEFM signal having a pulse duration of 3T is generated. Concerning the EFM signal having a pulse duration of 11T, the EQEFM signal having a pulse duration of 10T is generated. With regard to the EFM signal having a pulse duration of 3T, a period of xcex1=0.13T is added to the pulse duration of the EQEFM signal. The symbol xe2x80x9cPwxe2x80x9d represents the writing laser power.
The EQEFM signal corresponds to the laser emission level. Concerning the EFM pulse having a duration of (N)T, the EQEFM signal having a pulse duration of (Nxe2x88x921)T is generated. This is configured so in anticipation of a portion in which a pit is formed by thermal accumulation immediately after the laser emission is stopped.
Therefore, the relationship between the EFM signal and the formed pits P and lands L is such that the pulse duration is associated with the pit length and the land length, as shown in FIG. 16.
FIG. 15 shows a driving pulse generated when writing at a xc3x974 writing speed.
In the example shown in FIG. 15, the EQEFM signal has a pulse which basically has a duration of (Nxe2x88x920.5)T with respect to the EFM pulse having a duration of (N)T (in the drawing, xcex8=0.5T). For example, concerning the EFM signal with a pulse duration of 4T, the EQEFM signal having a pulse duration of 3.5T is generated.
In this case, an increased power portion expressed by xcex94P is added to period ODT at the leading edge of the pulse. Hereinafter, the increased power portion or a pulse for forming the increased power portion is referred to as an overdrive pulse.
FIG. 17 shows pits and lands formed by a laser which is driven to emit light based on a driving pulse generated by the method shown in FIG. 14. FIG. 18 shows pits and lands formed by a laser which is driven to emit light based on a driving pulse generated by the method shown in FIG. 15.
FIGS. 17 and 18 show the laser power controlled by driving pulses generated based on the EFM signal shown in FIG. 16. The symbol xe2x80x9cPwxe2x80x9d represents the writing laser power, and the symbol xe2x80x9cPrxe2x80x9d represents the reading laser power. FIGS. 17 and 18 show the formed pits P and lands L.
Referring to FIGS. 17 and 18, period A and period B each indicate a delay from the start of the laser beam emission until the formation of the pit P starts. Period a and period b each indicate a delay from the termination of the laser emission until the formation of the pit P is completed.
Recently, recording rates have been increased. Concerning CD-R and CD-RW, the recording rates have been further increased. For example, recording at a xc3x978 speed has been achieved.
Upon recording at the xc3x978 speed, when the laser power is controlled by the method shown in FIG. 14 or by the method shown in FIG. 15, intersymbol interference occurs, and jitter of the recording data increases. In the worst case, the recording data cannot be read.
Accordingly, it is an object of the present invention to implement laser power control so that appropriate recording is performed at a fast recording rate.
According to one aspect of the present invention, there is provided a recording apparatus. The recording apparatus includes a laser unit for performing laser beam irradiation with a supplied driving pulse to form a recording data row on a recording medium. The data row is formed of pits and lands, in which the lands are between the pits and the pits are before and after the lands. A driving pulse generator generates a first pulse in accordance with recording data, a second pulse to be combined with the leading edge of the first pulse, and a third pulse to be combined with the trailing edge of the first pulse. The driving pulse generator synthesizes the driving pulse by combining the first, second, and third pulses. A pulse generation controller controls at least one of the first, second, and third pulses generated by the driving pulse generator so that one of the level and the pulse duration thereof is varied in accordance with the length of at least one of the formed pits and lands.
Preferably, the pulse generation controller variably sets, in accordance with a predetermined recording condition, the level of each of the second and third pulses.
The pulse generation controller may variably set, in accordance with a predetermined recording condition, the pulse duration of each of the second and third pulses within a range of 0T to 3T.
The pulse generation controller may variably set, in accordance with the length of at least one of the pit and the land immediately formed before, the pulse duration of at least one of the first, second, and third pulses.
The recording apparatus may further include a detector for detecting the length of the land immediately formed before the formed pit. The pulse generation controller may vary the pulse duration of the first pulse in accordance with the detected land length.
The detector may detect the length of the formed pit. The pulse generation controller may vary the pulse duration of the first pulse in accordance with the detected pit length.
The detector may detect the length of the land formed immediately after the formed pit. The pulse generation controller may vary the pulse duration of the first pulse in accordance with the detected land length.
The recording apparatus may further include a switch for switching the operation of the driving pulse generator so that at least one of the first, second, and third pulses generated by the driving pulse generator is not output. The pulse generation controller may control the switch in accordance with a speed at which the recording data row is formed on the recording medium.
The recording medium may be a write once optical disk. The pulse generation controller may control the switch so that the third pulse is not output when the optical disk is rotated at a linear velocity not greater than a four-times speed of a reference linear velocity.
According to another aspect of the present invention, there is provided a recording method. The recording method includes a generating step of generating a first pulse in accordance with recording data, a second pulse to be combined with the leading edge of the first pulse, and a third pulse to be combined with the trailing edge of the first pulse, in which one of the level and the pulse duration is varied in accordance with the length of at least one of formed pits and lands. In a synthesizing step, a driving pulse is synthesized by combining the first, second, and third pulses. In a forming step, a recording data row is formed on a recording medium by performing laser beam irradiation using the driving pulse. The recording data row is formed of the pits and the lands, in which the lands are between the pits and the pits are before and after the lands.
The recording method may further include a control step of controlling, in the generating step of generating the first, second, and third pulses, the second and third pulses not to be generated in accordance with a speed at which the recording data row is formed on the recording medium.
Accordingly, thermal interference between codes (pits and lands) to be recorded is reduced. When recording at a fast recording rate, such as a xc3x978 speed, appropriate pits and lands are formed in which a sufficient read margin is obtained. A reduction in recording jitter improves the quality of recording data. Recording in accordance with a recording environment is performed.